import graph; import palette; int n=256; pen[] Palette=BWRainbow(); real w(real w0, real z0, real z) {return w0*sqrt(1+(z/z0)^2);} real pot(real lambda, real w0, real r, real z) { real z0=pi*w0^2/lambda, kappa=2pi/lambda; return exp(-2*(r/w(w0,z0,z))^2)*cos(kappa*z)^2; } picture make_field(real lambda, real w0) { real[][] v=new real[n][n]; for(int i=0; i < n; ++i) for(int j=0; j < n; ++j) v[i][j]=pot(lambda,w0,i-n/2,abs(j-n/2)); picture p=new picture; size(p,250,250,IgnoreAspect); real xm=-n/lambda, ym=-n/(2*w0), xx=n/lambda, yx=n/(2*w0); image(p,v,(xm,ym),(xx,yx),Palette); xlimits(p,xm,xx); ylimits(p,ym,yx); xaxis(p,"{\Large $z/\frac{\lambda}{2}$}",BottomTop,LeftTicks); yaxis(p,"{\Large $r/w_0$}",LeftRight,RightTicks); label(p,format("{\LARGE $w_0/\lambda=%.2f$}",w0/lambda),point(p,NW),5N); return p; } picture p=make_field(160,80); picture q=make_field(80,80); picture r=make_field(16,80); picture s=make_field(2,80); real margin=1cm; add(p.fit(),(0,0),margin*NW); add(q.fit(),(0,0),margin*NE); add(r.fit(),(0,0),margin*SW); add(s.fit(),(0,0),margin*SE);